OSI stands for the term "Open System Interconnection".

OSI is a ISO standard used for communications all over the world. It helps to define a network framework so that companies and institutions can then implement a protocol in the now standard seven layers. The seven layers are a hierarchy with controls and functions being passed downwards through the layers, and then going back in a loop. Due to some of to some proprietary issues OSI has never become the universal communications standard it was once fated to be. It has now been relegated as a basic model for other protocols to learn from.